1. Field of the Invention
The present invention relates generally to a fuser apparatus for a printing machine and more specifically to a fuser roll in which a journal member is secured simply and effectively to a roller or tubular member.
2. Description of the Prior Art
In imaging systems commonly used today, a charge retentive surface is charged to a uniform potential and thereafter exposed to a light source for selectively discharging the charge retentive surface to form a latent electrostatic image thereon. The image may comprise either the discharged portions or the charged portions of the charge retentive surface. The light source may comprise any well known device such as a light lens scanning system or a laser beam. Subsequently, the electrostatic latent image on the charge retentive surface is rendered visible by developing the image with developer powder referred to in the art as toner. The most common development systems employ developer which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development, the toner particles are attracted from the carrier particles by the charged pattern of the image areas of the charge retentive surface to form a powder image thereon. This toner image may be subsequently transferred to a support surface, such as plain paper, to which it may be permanently affixed by heating and/or applying pressure.
In order to fix or fuse the toner material onto a support member with heat, the temperature of the toner material is elevated to a point at which constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent onto the fibers or pores of the support members or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member.
One approach to thermal fusing of toner material images onto the supporting substrate has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members, at least one of which is internally heated. During operation of a fusing system of this type, the support member, to which the toner images are electrostatically adhered, is moved through a nip formed between the rolls with the toner image contacting the heated fuser roll to thereby effect heating of the toner images within the nip. Typically, at least one of the roller members, such as the internally heated roller member, has endcaps fitted to the opposing ends thereof. Each endcap preferably includes a shaft, the shaft being rotatably mounted to a bearing member.
In one known embodiment of a fuser roller, the roller member and the endcaps are constructed from a similar conductive material, such as aluminum. Indeed, in one example the roller member and the endcaps are cast as a single piece. It has been found, however, that using the same material to construct both the roller member and the endcaps is disadvantagious. In particular, when the same material is used to construct the fuser roller, the heat distribution is the same across the entire fuser roller so that, during the fusing process, the heat dissipation is the same for the roller member and the endcaps. This is undesirable since, under ideal conditions, a relatively high level of heat is dissipated by the roller member, to facilitate fusing, and a relatively low level of heat is dissipated by the endcaps, to minimize wear on the bearing member. Various disclosures of fusing apparatuses, capable of reducing heat dissipation in the endcaps, are briefly summarized below:
U.S. Pat. No. 3,437,032 PA1 Patentee: Manghirmalani et al. PA1 Issued: Apr. 8, 1969 PA1 U.S. Pat. No. 4,538,052 PA1 Patentee: Asanuma et al. PA1 Issued: Aug. 27, 1985 PA1 U.S. Pat. No. 4,618,240 PA1 Patentee: Sakurai et al. PA1 Issued: Oct. 21, 1986 PA1 Japanese Application No. 56-73514 PA1 Application Filing Date: May 18, 1981 PA1 Japanese Publication No. 57-189170 PA1 Publication Date: Nov. 20, 1982 PA1 Inventor: Itou
U.S. Pat. No. 4,538,052 discloses a "prior art" fuser roller and an improvement thereof. The known fuser roller comprises an aluminum roller member with stainless steel endcaps. Preferably the endcaps are fitted to the aluminum roller member under pressure using frictional heat. U.S. Pat. No. 3,437,032 discloses a fuser roll which is similar to the above-mentioned prior art fuser roll in that stainless steel endcaps are shown secured to the ends of a nickel-plated copper tube. To avoid the technical difficulties in securing stainless steel to another metal, as well as the relatively high manufacturing costs associated with such securing, U.S. Pat. No. 4,538,052 discloses an improved fuser roller in which a pair of bearings, having outer races made of heat-resistant resin, are fitted into end portions of the aluminum cylinder under pressure to support the cylinder so that the outer races and cylinder turn as one unit. The heat-resistant resins are more economical than the metal members, and the races can easily be fit into both end portions of the aluminum cylinder by merely pressing them against both end portions of the cylinder.
U.S. Pat. No. 4,618,240 discloses a fuser roller having a roller with shafts at the end thereof. The shafts are rotatably mounted in bearings and are fitted with heat resistive sleeves. The heat resistive sleeves are constructed of heat-intercepting material and disposed between the shafts and bearings to prevent heat transfer between the ends of the roller and the bearings.
Japanese application No. 57-189170 discloses a heater roller made of thin cylinders. A roller rotation driving member is fitted to both ends of the thin cylinders via elastic members, such as silicon rubber members, to reduce heat loss from the thin cylinders through the shaft.
While the fuser rolls of U.S. Pat. No. 4,538,052 and Japanese application No. 57-189170 may effectively isolate a roller member from a journal, these fuser rolls are not necessarily easy to construct since the endcap components must be pressed or forced into end portions of the roller member. In particular, manufacturing costs for these rolls can be needlessly high since special tooling is required to achieve the pressing or forcing. Moreover, while both the prior art fuser roll of U.S. Pat. No. 4,538,052 and the fuser roll of U.S. Pat. No. 3,437,032 possess designs that are simple and durable, they too can be needlessly expensive to manufacture since fitting an endcap of one material to a roller of another material can be technically difficult. It would be desirable to provide a fuser roller that is both cheap and easy to manufacture as well as simple and durable in design.